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Barrel/cylinder ratio - sorry for yet another thread

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Barrel/cylinder ratio - sorry for yet another thread

Unread postAuthor: Ianbuckwell » Sat May 10, 2014 7:45 am

If using a 150psi, iirc the barrel to cylinder ratio should be about 1:1, do you just use this figure or add say a 10% gain to the cylinder just to ensure your projectile gets at least enough air??? I guess it can't do any harm apart from waste a bit of air.

Was given the idea of an old fridge compressor by Smirkjacksrevenge, so if I can get one of these air over 150psi won't be a problem, as it sounds like shock pumps are a lot of hard work, especially if you have around 1 litre (sorry don't know it in cubic inches) primary tank. Just need to find an old fridge :)
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Re: Barrel/cylinder ratio - sorry for yet another thread

Unread postAuthor: Gippeto » Sat May 10, 2014 8:30 am

Model it with ggdt. Swap variables for performance until you're happy....then build to that "spec".

http://www.thehalls-in-bfe.com/GGDT/
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Re: Barrel/cylinder ratio - sorry for yet another thread

Unread postAuthor: Ianbuckwell » Sat May 10, 2014 8:34 am

Only have access via phone and Nexus 7 have to go see my mum and use her computers, are there any instructions around as i will be have a lot more questions, i am sure!!
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Re: Barrel/cylinder ratio - sorry for yet another thread

Unread postAuthor: jackssmirkingrevenge » Thu May 15, 2014 4:59 am

To answer your PM in public so others may benefit:

Shock pumps are a real pain in the posterior for anything bigger than a pen gun.

Think about getting a floor pump: http://www.amazon.co.uk/Airace-Infinity ... 325&sr=8-8

If you want more power, bigger is always better.

Here's a simulation at 200 psi with a 12mm bearing, 24 inch barrel and 10 inch long 0.75 inch diameter firing chamber:

ggdt.jpg


There you're doing 36 ft lbs. If I up the pressure to 300 psi, GGDT predicts 52 ft lbs. Moar pressue = moar power, no two ways about it.
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Re: Barrel/cylinder ratio - sorry for yet another thread

Unread postAuthor: Ianbuckwell » Thu May 15, 2014 8:37 am

Just seen this and it has answered alot of my questions in other thread, I need to increase bore and pressure.

Does barrel length (thinking) either way of 24" by 8 under or 12" over have much influence on power output, I am guessing longer rthe barrel better the accuracy or is this not true?
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